Atomic layer etching of tungsten and other metals

ABSTRACT

Provided herein are methods of atomic layer etching (ALE) of metals including tungsten (W) and cobalt (Co). The methods disclosed herein provide precise etch control down to the atomic level, with etching a low as 1 Å to 10 Å per cycle in some embodiments. In some embodiments, directional control is provided without damage to the surface of interest. The methods may include cycles of a modification operation to form a reactive layer, followed by a removal operation to etch only this modified layer. The modification is performed without spontaneously etching the surface of the metal.

CROSS REFERENCE TO REFLATED APPLICATION

This application claims the benefit of priority to U.S. ProvisionalApplication No. 62/207,250, title “ATOMIC LAYER ETCHING OF TUNGSTEN ANDOTHER METALS,” filed Aug. 19, 2015, all of which is incorporated hereinby this reference in its entirety and for all purposes.

BACKGROUND

Semiconductor fabrication processes often involve deposition of metals,such as tungsten, into features to form contacts or interconnects. Asdevices shrink, features become smaller and harder to fill, particularlyin advanced logic and memory applications. Fabrication of metalcontacts, metal interconnects, or other metal structures may involveetch back of the metal.

One aspect of the disclosure relates a method of etching a metal on asubstrate, the metal being selected from tungsten (W) and cobalt (Co).It involves (a) exposing a surface of the metal to a halide chemistry toform a modified halide-containing surface layer; and (b) applying a biasvoltage to the substrate while exposing the modified halide-containingsurface layer to a plasma to thereby remove the modifiedhalide-containing surface layer. In some embodiments, the plasma is anargon plasma and the bias voltage in (b) is between about 50 Vb and 80Vb.

In some implementations, the modification operation of (a) includesexposing the surface of the metal to a plasma. If a plasma is usedduring (a), a bias may or may not be applied to the substrate during(a). The substrate temperature may be maintained to preventspontaneously etching the metal. For example, in some embodiments, (a)involves exposing a tungsten surface to a chlorine-containing plasma attemperatures less than 150° C. to prevent spontaneous etch of thetungsten by the plasma.

Also provided is an apparatus for processing semiconductor substrates,the apparatus including: a process chamber comprising a showerhead and asubstrate support, a plasma generator, and a controller having at leastone processor and a memory, wherein the at least one processor and thememory are communicatively connected with one another, the at least oneprocessor is at least operatively connected with flow-control hardware,and the memory stores machine-readable instructions for: (i) introducinga halide-containing gas to modify a tungsten surface; and (ii)introducing an activation gas and igniting a plasma to etch at leastpart of the modified surface of tungsten. In some implementations, thememory further stores machine-readable instructions for igniting aplasma during (i). In some embodiments, the halide-containing gas is achlorine-containing gas and memory further stores machine-readableinstructions for maintaining a temperature of the substrate support atless than 150° C. during (i).

These and other aspects of the disclosure are discussed further below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an example of atomic layer etching(ALE) of film on a substrate.

FIG. 2 is a process flow diagram depicting operations performed inaccordance with certain disclosed embodiments.

FIG. 3 is a graph of calculated normal incident sputter yield oftungsten using argon ions.

FIG. 4 shows graphs qualitatively illustrating etch rate for ALE as afunction of chlorination time and argon removal step time for an ALEprocess including plasma chlorination and removal by an activated argongas.

FIG. 5 is a graph of experimental data collected for etch rates oftungsten over chlorination bias power.

FIG. 6 is a graph comparing etch rates of tantalum etches using argonremoval only versus argon removal following plasma chlorination asfunctions of bias voltage.

FIG. 7 is a schematic diagram of an example process apparatus forperforming certain disclosed embodiments.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the presented embodiments. Thedisclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Tungsten metal is used in semiconductor industry for its relatively lowresistivity and electromigration properties. It is currently used as alow-resistive metallic interconnect, and is being tested for use inemerging memory applications. A number of applications require etchingtungsten, and it can be challenging etch in controlled manner withatomic precision. For example, the uniformity of tungsten etched mayneed to be within 1 nm across the wafer, feature-to-feature, and at thesurface, referring the smoothness. When etching tungsten in features,small openings (e.g., less than 20 nm) and loading effects in whichdifferent feature sizes have different etch rates provide additionalchallenges. Conventional etching using a continuous process does notoffer sufficient etch control for advanced applications of tungstenetching.

In another example, cobalt may be used as an interconnect material inplace of copper. Replacing copper with cobalt introduces its ownprocessing challenges, including, for example, etching of cobalt.Currently, Co can be etched back using a wet process. However, the wetetch rate can be variable with changes in feature size. In addition, thewet process may cause the surface of the substrate to be significantlyrough, e.g., rougher than a surface etched by a dry process. Etchingback Co using anisotropic plasma etching has proven to be very difficultas the etch products are almost all or often non-volatile. Non-volatileetch products may result in re-deposition of the etch products ordefects on other exposed components of the substrate. These re-depositeddefects contain metal and are difficult if not impossible to remove. Asa result, plasma etching of this metal is often conventionally achievedwith physical sputtering, which unfortunately leads to etch selectivityso poor that the process cannot be used in production.

Provided herein are methods of atomic layer etching (ALE) of metalsincluding tungsten (W), titanium (Ti), and cobalt (Co), as well as ALEetching of metal nitrides and metal oxides including tungsten nitride(WN), tantalum oxide (Ta₂O₃), tantalum nitride (TaN), titanium oxide(TiO), and titanium nitride (TiN), and ALE etching of the metalloidgermanium (Ge). References herein to metals refer to elemental forms ofthe metals. Similarly, unless otherwise specified, germanium refers toelemental germanium. References herein to metal oxides and metalnitrides refer to oxide and nitride compounds of the metals withoutbeing limited to a particular stoichiometric ratio and include compoundssuch as oxynitrides. It is understood that there may be some amount ofimpurities present in a layer or film of a metal, metal compound orgermanium.

The methods disclosed herein provide precise etch control down to theatomic level, with etching a low as 1 Å to 10 Å per cycle in someembodiments. In some embodiments, directional control is providedwithout damage to the surface of interest.

ALE is a technique that removes thin layers of material using sequentialself-limiting reactions. Generally, ALE may be performed using anysuitable technique. Examples of atomic layer etching techniques aredescribed in U.S. Pat. No. 8,883,028, issued on Nov. 11, 2014; and U.S.Pat. No. 8,808,561, issued on Aug. 19, 2014, which are hereinincorporated by reference for purposes of describing example atomiclayer etching techniques. In various embodiments, ALE may be performedwith plasma, or may be performed thermally. The concept of an “ALEcycle” is relevant to the discussion of various embodiments herein.Generally an ALE cycle is the minimum set of operations used to performan etch process one time, such as etching a monolayer. The result of onecycle is that at least some of a film layer on a substrate surface isetched. Typically, an ALE cycle includes a modification operation toform a reactive layer, followed by a removal operation to remove or etchonly this modified layer. The cycle may include certain ancillaryoperations such as sweeping one of the reactants or byproducts.Generally, a cycle contains one instance of a unique sequence ofoperations. As an example, an ALE cycle may include the followingoperations: (i) delivery of a reactant gas, (ii) purging of the reactantgas from the chamber, (iii) delivery of a removal gas and an optionalplasma, and (iv) purging of the chamber. According to variousembodiments, etching may be performed conformally or nonconformally.

FIG. 1 shows two example schematic illustrations of an ALE cycle.Diagrams 171 a-171 e show a generic ALE cycle. In 171 a, a substrate isprovided. In 171 b, the surface of the substrate is modified. In 171 c,the chemical used to modify the substrate is purged. In 171 d, themodified layer is being etched. In 171 e, the modified layer is removed.Similarly, diagrams 172 a-172 e show an example of an ALE cycle foretching a tungsten film. In 172 a, a tungsten layer on a substrate isprovided, the layer including many tungsten atoms. In 172 b, reactantgas chlorine is introduced to the substrate, which modifies the surfaceof the tungsten layer. The schematic in 172 b shows that some chlorineis adsorbed onto the surface of the tungsten as an example. In 172 c,the reactant gas chlorine is purged from the chamber. In 172 d, an argonremoval gas is introduced with a directional plasma, as indicated by theAr⁺ plasma species and arrows, to remove the modified surface of thesubstrate. The activated etching involves the use of inert ions (e.g.,Ar⁺) operating with energy below the sputtering threshold to energizethe adsorb species (in this example, Cl species) to etch away thesubstrate one monolayer at a time. During this operation, a bias isapplied to the substrate to attract ions toward it. In 172 e, thechamber is purged and the byproducts are removed.

ALE etches uniformly due to the self-limiting nature of the surfacereactions. Thus, ALE processes provide high control over the etchingoperations such that the amount of material removed in each cycle islimited and not etched too quickly so as to prevent completely etchingof material from the surface of the feature.

Disclosed embodiments involve modification of a metal, metal oxide,metal nitride, or germanium surface by modification of the surface witha halide chemistry and exposure to an activation gas to remove themodified surface.

ALE of metals and metal compounds may present several challenges,including a modification chemistry that interacts with the surface toform a modified layer without spontaneously etching the surface. Theself-limiting behavior described above with respect to FIG. 1 does notoccur if the modification reactant spontaneously etches the tungstensurface. Because halides are used in conventional continuous etching oftungsten and other metals, it was unexpected that they could be used forALE. No etching may occur if the modification chemistry does not form amodified layer. While chlorination has been used to modify surfaces suchas silicon in ALE processes, it has been thought that the chlorinationof such surfaces occurs due to the electronegativity mismatch betweenchlorine and silicon such that chlorine attracts an electron from thesilicon, weakening the underlying bond. It was not clear that such amechanism could work with metal surfaces such as tungsten.

The materials that may be etched by the embodiments disclosed hereininclude W, Ti, and Co, tungsten nitrides (WN), tantalum oxides(TaO_(x)), tantalum nitrides (TaN_(x)), titanium oxides (TiO_(x)),titanium nitrides (TiN_(x)), and Ge. In the case of compound films, xmay be any appropriate non-zero positive number.

As shown in the example of FIG. 1 at 171 b, a surface to be etched isexposed to a modification chemistry that interacts with the surface toform a modified layer. In the methods disclosed herein, a halidemodification chemistry is employed. The halide modification chemistrymay include a bromine (Br)-containing, chlorine (Cl)-containing, orfluorine (F)-containing compound. Examples of Br-containing modificationchemistries include dibromine (Br₂) and hydrogen bromide (HBr). Examplesof Cl-containing modification chemistries include chlorine (Cl₂), borontrichloride (BCl₃) and silicon tetrachloride (SiCl₄). Examples offluorine-containing modification chemistries include sulfur hexafluoride(SF₆), carbon tetrafluoride (CFA and silicon tetrafluoride (SiF₄). Insome embodiments, a halide modification chemistry may include two ormore halogen-containing compounds. As an example, a Cl₂/BCl₃ mixture maybe used to prevent or reduce oxidation during ALE.

The halide modification chemistry interacts with the surface withoutspontaneously etching it. Nitrogen trifluoride (NF₃) is generally toostrong to be employed in ALE of the surfaces disclosed herein as itspontaneously etches rather than modifies the surface. The successfuluse of SF₆ for ALE of tungsten was unexpected, as it was expected toalso spontaneously etch tungsten. Without being bound by a particulartheory, it is believed that SF₆ and CF₄ may modify the surface byforming an adsorbed polymer layer on it, thereby allowing theself-limiting synergistic etch that ALE provides.

In another example, in some embodiments, a boron-containing compound maybe used to deposit a thin boron-containing layer on a surface. Forexample, U.S. patent application Ser. No. 14/794,285, filed Jun. 24,2015, incorporated by reference herein, discloses Co etch by forming athin BCl_(x) layer on Co. An activated activation gas, plasma, andactivated halides from the surface of the substrate as deposited mayperform an atomic layer etch. The BCl₃ used in this approach can bereplaced with other chemistry that can provide comparable deposition andactivation functions, such as boron tribromide (BBr₃) and borontriiodine (BI₃).

According to various embodiments, the modification operation may includeexposure to a plasma. Exposure to a plasma may increase throughput byincreasing the rate at which the surface is modified. For example,plasma can be used to speed up the modification by producing highlyreactive radicals and/or other energetic species to induce the surfacemodification. However, certain plasma conditions may facilitateundesirable spontaneous etching. As discussed further below, a plasmagenerated from Cl₂ may spontaneously etch the tungsten at temperaturesgreater than 150° C.

Depending on the surface to be modified and the modification chemistry,a plasma may be used to modify surfaces that do not undergo modificationin the absence of a plasma. For example, while chlorine canspontaneously form a bond with silicon atoms of a silicon surface andgermanium atoms of a germanium surface such that a plasma is optional,tungsten surfaces will generally not undergo chlorination unless thereis sufficient energy to generate Cl atoms from Cl₂ or other Cl source.Plasma chlorination generates Cl atoms. Thermal energy may also besufficient to break apart Cl₂, though at temperatures higher thantypical thermal budgets.

If a plasma is employed during the modification operation, a bias may ormay not be used. In many cases, a bias is not used to avoid ionbombardment and sputtering. However, a small bias may be useful toprovide directionality to the modification species. For example, asdescribed in concurrently-filed patent application U.S. Pat. No. ______(Attorney Docket 3685/LAMRP203), which is incorporated by referenceherein, a low bias power may be used in ALE of a tungsten in a recessedfeature that is partially filled with tungsten. The low bias preventssputtering while allowing modification species to be adsorbed on thesurface of the metal. The bias can facilitate the modification speciesentering a seam formed opening in the feature, for example. Examplebiases during a modification operation may range from 0 Vb to 100 Vb, 0Vb to 50 Vb, or 0 Vb to 20 Vb.

The terms “bias power” and “bias voltage” are used herein to describe abias that is applied to the pedestal. A threshold bias power refers orthreshold bias voltage refers to the maximum voltage of the bias appliedto a pedestal before material on the surface of a substrate on thepedestal is sputtered. The threshold bias power therefore depends inpart on the material to be etched, the gas used to generate plasma,plasma power for igniting the plasma, and plasma frequency. Bias poweror bias voltage as described herein is measured in volts, which areindicated by the unit “V” or “Vb”, where b refers to bias.

FIG. 2 provides a process flow diagram depicting operations in a methodin accordance with disclosed embodiments. In operation 202 of FIG. 2, asubstrate is provided to a chamber. The substrate may be a siliconwafer, e.g., a 200-mm wafer, a 300-mm wafer, or a 450-mm wafer,including wafers having one or more layers of material such asdielectric, conducting, or semi-conducting material deposited thereon. Apatterned substrate may have features such as vias or contact holes,which may be characterized by one or more of narrow and/or re-entrantopenings, constrictions within the features, and high aspect ratios. Thefeatures may be formed in one or more of the above described layers. Oneexample of a feature is a hole or via in a semiconductor substrate or alayer on the substrate. Another example is a trench in a substrate orlayer.

The substrate includes an exposed surface of a metal, metal oxide ormetal nitride film as described above. According to various embodiments,the exposed surface may be present on vertical surfaces (e.g., sidewallsof a feature), horizontal surfaces (e.g., blanket layers, field regions,or feature bottoms), or both. In some embodiments, for example, a metalmay be etched from a feature partially filled with the metal. In someembodiments, for example, a substrate includes a blanket layer of themetal or metal compound film. The substrate may further include apatterned mask layer previously deposited and patterned on thesubstrate. The material to be etched by ALE may have been previouslydeposited by any suitable such as atomic layer deposition (ALD),chemical vapor deposition (CVD), sputtering and other physical vapordeposition (PVD) methods, or electro or electroless plating.

In operation 204, the substrate is exposed to a halide chemistry tomodify the exposed metal or metal compound surface of the substrate. Thehalide chemistry may be provided as a gas or as a plasma. In someembodiments, reactive or activated species may be provided, e.g., atomicspecies, radicals, or high energy molecules. Activation may includeplasma activation, thermal activation, ultraviolet activation, and thelike. For example, in some embodiments, a gas may be activated byexposure to heat, radiation, or other energy source prior to enteringthe chamber or while in the chamber. In some embodiments, atomic orradical species may be delivered to the chamber, for example, from aremote plasma generator.

The modification operation forms a thin, reactive surface layer with athickness that is more easily removed than un-modified material.According to various embodiments, halide species may adsorb onto orreact with the exposed metal or metal compound surface to thereby modifyit. Example halide chemistries are described above and include Br₂, HBr,Cl₂, BCl₃, SiCl₄, SF₆, CF₄, and SiF₄. According to various embodiments,these may be supplied to the chamber as a gas, either alone or with acarrier gas or other gas. Examples of carrier gases include nitrogen(N₂), argon (Ar), neon (Ne), helium (He), and combinations thereof Insome embodiments, hydrogen (H₂) may be added to balance theconcentration of halide species.

The particular halide chemistry may be chosen based on the material tobe etched, with a chemistry that can be modify the surface to be etchedchosen. In addition, the chemistry may be chosen to tune the etch rate,control over the amount of material removed, selectivity to anunderlying layer or another exposed material on the substrate, and tolimit oxidation.

For example, fluorine-containing chemistries result in faster etch thanchlorine-based chemistries, with a few monolayers etched per cycle insome embodiments. This can be advantageous to increase throughput wherethere is a substantial amount of material to be etched. In applicationsin which very precise control of removal may be appropriate, achlorine-containing chemistry may be used. Selectivity may also becontrolled by the halide modification chemistry. For example Cl₂ orCl₂/BCl₃ for metal etch is highly selectivity to dielectrics like SiN orSiO, so mass preservation is better with those chemistries. In someembodiments, the methods include using a mixture of a Cl₂ and aboron-containing compound, such as BCl₃. Without being bound aparticular theory, it is believed that the addition of boron may preventunwanted oxidation of a surface. However, too much boron may lead todeposition. In some embodiments, the Cl₂/BCl₃ mixture is between 0.5%and 10% (volumetric) BCl₃, e.g., about 5% BCl₃.

If plasma modification is employed, a plasma may be generated in thechamber from the gas. This may generate various activated species fromthe halide-containing gas. References herein to a halide-containing gasor halide chemistry are understood to include species generated fromsuch a gas. In some embodiments, the plasma may be controlled such thatthe activated species in the chamber during operation 204 are primarilyor substantially radical species. In some embodiments, essentially noionic species are in the chamber. This may facilitate chemicalmodification, rather than etching, of the substrate surface. However, asdescribed above, in some embodiments, a bias may be employed to attractmodification species. In such embodiments, the plasma may be controlledsuch that there are low energy ionic species present.

Using a bias in the modification operation allows control of the depthof the modification and the subsequent removal. This can be advantageousfor etching in high aspect ratio features, and offers control overwhether or not the ALE penetrates into a feature or substantiallyremains on the field and upper edges of a feature.

In some embodiments, a purge may be performed after a modificationoperation. In a purge operation, non-surface-bound active modificationspecies may be removed from the chamber. This can be done by purgingand/or evacuating the process chamber to remove the modification gas,without removing the adsorbed layer. The species generated in a plasmacan be removed by extinguishing the plasma and allowing the remainingspecies to decay, optionally combined with purging and/or evacuation ofthe chamber. Purging can be done using any inert gas such as N₂, Ar, Ne,He and their combinations.

In operation 206, the modified layer is removed from the substrate usingan activated removal gas, such as an activating gas, sputtering gas, orchemically reactive gas. For example, argon may be used. In a removaloperation, the substrate may be exposed to an energy source (e.g.activating or sputtering gas or chemically reactive species that inducesremoval), such as argon or helium, to etch the substrate. In someembodiments, the removal operation may be performed by ion bombardment.

In embodiments in which ion bombardment is used, the ALE is directionaland etches the horizontal surfaces preferentially over vertical surfacessuch as sidewalls. However, in some embodiments, removal may beisotropic.

The amount of removal gas may be controlled such as to etch only atargeted amount of material. In various embodiments, the pressure of thechamber may vary between the modification and removal operations. Thepressure of the removal gas may depend on the size of the chamber, theflow rate of the removal gas, the temperature of the reactor, the typeof substrate, the flow rate of any carrier gases, and the amount ofmaterial to be etched.

During removal, a bias may be optionally applied to facilitatedirectional ion bombardment. The bias power is selected to preventsputtering but allow the removal gas to etch the material. The biaspower may be selected depending on the threshold sputter yield of theactivated removal gas with the metal or metal-containing compound filmon the substrate. Sputtering as used herein refers physical removal ofat least some of a surface of a substrate. Ion bombardment refers tophysical bombardment of a species onto a surface of a substrate.

FIG. 3 shows an example sputter yield calculated based on “EnergyDependence of the Yields of Ion-Induced Sputtering of Monatomic Solids”by N. Matsunami, Y. Yamamura, Y. Itikawa, N. Itoh, Y. Kazumata, S.Miyagawa, K. Morita, R. Shimizu, and H. Tawara, IPPJ-AM-32 (Institute ofPlasma Physics, Nagoya University, Japan, 1983).

The figure shows the calculated normal incidence sputter yield oftungsten with argon atoms versus argon ion energy (or threshold biaspower). The calculation used a value of 32 eV for the sputter threshold.Slightly above the threshold, namely at 40 eV argon ion energy, thesputter yield is seem to be about 0.001 atoms/ion. However, at 80 eV ionenergy, it has increased by a factor of 30. This example curve indicatesthe maximum argon ion energy sufficient to etch the metal whilepreventing sputtering of argon on the substrate. While FIG. 3 provides aqualitative representation of a sputter threshold curve, a sputterthreshold may be experimentally determined for a particular system andmaximum tolerable sputter yield. For one system, sputtering of tungstenis observed at 80 Vb for argon ions. As such, the bias power duringtungsten removal using argon ions may be set at less than about 80 Vb,or less than about 50 Vb, or between about 50 Vb and 80 Vb. In someembodiments, operation 206 may be performed above the threshold biaspower if some small amount of sputtering is tolerable. There may also bea removal threshold voltage, below which removal does not occur,depending on the particular process. It should be noted that the sputterthreshold varies according to the metal, metal compound, or othermaterial to be etched.

Returning to FIG. 2, in some embodiments, the chamber may be purgedafter operation 206. Purge processes may be any of those used for apurge after operation 204 as discussed above.

As described herein, in operations where materials are introduced intothe chamber, in some embodiments involving atomic layer etch using aplasma, the reactor or chamber may be stabilized by introducing thechemistry into the chamber prior to processing the substrate or wafer.Stabilizing the chamber may use the same flow rates, pressure,temperatures, and other conditions as the chemistry to be used in theoperation following the stabilization. In some embodiments, stabilizingthe chamber may involve different parameters. In some embodiments, acarrier gas, such as N₂, Ar, Ne, He, and combinations thereof, iscontinuously flowed during operations 204 and 206. In some embodiments,a carrier gas is only used during operation 106. In some embodiments, acarrier gas is not flowed during removal.

Performing operations 204 and 206 may, in some embodiments, constituteperforming ALE once. If the material is not sufficiently etched,operations 204 and 206 may be repeated. In various embodiments, themodification and removal operations may be repeated in cycles, such asabout 1 to about 30 cycles, or about 1 to about 20 cycles. Any suitablenumber of ALE cycles may be included to etch a desired amount of film.In some embodiments, ALE is performed in cycles to etch about 1 Å toabout 50 Å of the surface of the layers on the substrate. In someembodiments, cycles of ALE etch between about 2 Å and about 50 Å of thesurface of the layers on the substrate.

If repeated, the chemistries and process conditions during operations204 and 206 may be constant or vary from cycle to cycle. For example, insome embodiments, a different halide chemistry may be used. As describedabove, fluorine-containing chemistries may be useful for faster etch,while chlorine-containing chemistries may provide more control. As suchit may be advantageous to vary the chemistry from cycle-to-cycle, forexample, to move from a more aggressive etch using a fluorine-containingchemistry to a less aggressive etch using a chlorine-containingchemistry. In some embodiments, the chemistry may be modified toward theend of an etch process to provide high selectivity to an underlyingmaterial. In another example, in some embodiments, the bias voltage maybe lowered toward the end of the etch process. For example, at 0.5 nm, 1nm, or other appropriate amount left to etch, the bias voltage may belowered. In some embodiments, the bias voltage may be modified to avoltage that provides high selectivity to an underlying material.

Process parameters can vary depending on the apparatus used as well asthe modification chemistry, removal species and material to be etched.In various embodiments, the plasma may be an inductively coupled plasmaor a capacitively coupled plasma or a microwave plasma. If a plasma isemployed during a modification operation, the power and pressure may becontrolled to prevent or reduce dielectric etch. As indicated above,silicon-containing dielectrics are susceptible to etch byfluorine-containing chemistries. As such, fluorine adsorption or othermodification is conducted at mild conditions; it can be useful tooperate in a low power regime to preserve mass. Higher pressure is alsobe beneficial in reducing unwanted dielectric etch.

Temperature may controlled to provide smooth surfaces. In someembodiments, when using a chlorine plasma, ALE of tungsten is performedat a temperature below about 150° C. At temperatures above about 150°C., tungsten may spontaneously etch in the presence of chlorine plasma.This can lead to etching during the chlorine-containing step as well asduring the subsequent Ar plasma, which can result in a process that iscloser to continuous etching than ALE. Moreover, because chlorineetching dominates, the resulting surface may be rough.

Power for an inductively coupled plasma may be set at between about 30 Wand about 1500 W. As indicated above, power may be set at a low enoughlevel so as not to cause direct plasma etching of the substrate. Exampleranges may be between 30 W and 500 W, or 30 W and 200 W. Power is givenfor a 300 mm wafer and scales with surface area. Example pressures maybe between 10 Torr to 80 Torr, or 30 Torr to 60 Torr. During the removaloperation, lower pressure, e.g., 2 mTorr to 90 mTorr may be used.

While the above description focuses on metal, metal oxide and metalnitride films, the methods disclosed herein may be used for ALE ofgermanium. In embodiments in which germanium is to be etchedanisotropically from a feature, it may be advantageous to oxidize thegermanium surface every n cycles to protect the sidewalls of the featurefrom being etched. This is because germanium is highly reactive.

EXAMPLES

ALE of Tungsten: FIG. 4 shows graphs qualitatively showing ALE etch rateas function of chlorination time and argon removal time for ALE etch oftungsten. The graphs in FIG. 4 demonstrate self-limiting behavior,indicating that the etch of tungsten is not spontaneous and that ALE wassuccessfully implemented. Plasma chlorination was employed.

Etch rate of tungsten was plotted against chlorination bias power foretch with chlorine adsorption and no argon ion bombardment, as well asfor an atomic layer etch (ALE) process with chlorine adsorption withargon ion bombardment. The results are plotted in FIG. 5. The dottedline depicts the etch rate of tungsten versus chlorination bias (e.g.,the bias power during chlorine adsorption) for a process involvingadsorbing chlorine and igniting a plasma at 900 W, and no argon ionbombardment. The solid line depicts the etch rate of tungsten versuschlorination bias for a process involving adsorbing chlorine andigniting a plasma at 900 W, followed by an argon ion bombardment with abias power of 60V. A chlorination bias threshold voltage as shown inFIG. 5 is at about 60V. Note where a chlorination bias is less than 60V,tungsten is not etched without using ion bombardment of argon. Where achlorination bias is greater than 60V, the etch rate of tungsten withoutargon ion bombardment is much lower than that of the process with argonion bombardment. These results suggest that argon ion bombardment may beused to modulate the etch rate of metals by ALE methods in variousembodiments whereby 1) chlorine is being adsorbed onto the tungstensubstrate without etching during chlorination, and 2) the bias powerduring ion bombardment of argon is controlled to reduce or preventphysical removal (or sputtering) by setting the bias power lower thanthe sputter threshold.

Further examples of ALE tungsten to facilitate feature fill are providedin concurrently filed U.S. patent application Ser. No. 14/830,683(Attorney Docket No. LAMRP203/3685-2US), which is incorporated byreference herein and for all purposes.

Tantalum Etch: Plasma chlorination followed by an Ar removal (ALEcycles) was employed to etch tantalum metal and compared to Ar removalonly. Results are plotted in FIG. 6, which shows no synergistic effect.Specifically, the chlorination of the ALE cycles did not improve etchrate. This indicates that ALE was unsuccessful.

Apparatus

Inductively coupled plasma (ICP) reactors which, in certain embodiments,may be suitable for atomic layer etching (ALE) operations and atomiclayer deposition (ALD) operations are now described. Such ICP reactorshave also been described in U.S. Patent Application Publication No.2014/0170853, filed Dec. 10, 2013, and titled “IMAGE REVERSAL WITH AHMGAP FILL FOR MULTIPLE PATTERNING,” hereby incorporated by reference inits entirety and for all purposes. Although ICP reactors are describedherein, in some embodiments, it should be understood that capacitivelycoupled plasma reactors may also be used.

FIG. 7 schematically shows a cross-sectional view of an inductivelycoupled plasma integrated etching and deposition apparatus 700appropriate for implementing certain embodiments herein, an example ofwhich is a Kiyo® reactor, produced by Lam Research Corp. of Fremont,Calif.. The inductively coupled plasma apparatus 700 includes an overallprocess chamber 724 structurally defined by chamber walls 701 and awindow 711. The chamber walls 701 may be fabricated from stainless steelor aluminum. The window 711 may be fabricated from quartz or otherdielectric material. An optional internal plasma grid 750 divides theoverall process chamber 724 into an upper sub-chamber 702 and a lowersub-chamber 703. In most embodiments, plasma grid 750 may be removed,thereby utilizing a chamber space made of sub-chambers 702 and 703. Achuck 717 is positioned within the lower sub-chamber 703 near the bottominner surface. The chuck 717 is configured to receive and hold asemiconductor substrate or wafer 719 upon which the etching anddeposition processes are performed. The chuck 717 can be anelectrostatic chuck for supporting the wafer 719 when present. In someembodiments, an edge ring (not shown) surrounds chuck 717, and has anupper surface that is approximately planar with a top surface of thewafer 719, when present over chuck 717. The chuck 717 also includeselectrostatic electrodes for chucking and dechucking the wafer 719. Afilter and DC clamp power supply (not shown) may be provided for thispurpose. Other control systems for lifting the wafer 719 off the chuck717 can also be provided. The chuck 717 can be electrically chargedusing an RF power supply 723. The RF power supply 723 is connected tomatching circuitry 721 through a connection 727. The matching circuitry721 is connected to the chuck 717 through a connection 725. In thismanner, the RF power supply 723 is connected to the chuck 717.

Elements for plasma generation include a coil 733 is positioned abovewindow 711. In some embodiments, a coil is not used in disclosedembodiments. The coil 733 is fabricated from an electrically conductivematerial and includes at least one complete turn. The example of a coil733 shown in FIG. 7 includes three turns. The cross-sections of coil 733are shown with symbols, and coils having an “X” extend rotationally intothe page, while coils having a “” extend rotationally out of the page.Elements for plasma generation also include an RF power supply 741configured to supply RF power to the coil 733. In general, the RF powersupply 741 is connected to matching circuitry 739 through a connection745. The matching circuitry 739 is connected to the coil 733 through aconnection 743. In this manner, the RF power supply 741 is connected tothe coil 733. An optional Faraday shield 749 is positioned between thecoil 733 and the window 711. The Faraday shield 749 is maintained in aspaced apart relationship relative to the coil 733. The Faraday shield749 is disposed immediately above the window 711. The coil 733, theFaraday shield 749, and the window 711 are each configured to besubstantially parallel to one another. The Faraday shield 749 mayprevent metal or other species from depositing on the window 711 of theprocess chamber 724.

Process gases (e.g., carrier gases, halogen-containing gases, argon,etc.) may be flowed into the process chamber through one or more maingas flow inlets 760 positioned in the upper sub-chamber 702 and/orthrough one or more side gas flow inlets 770. Likewise, though notexplicitly shown, similar gas flow inlets may be used to supply processgases to a capacitively coupled plasma processing chamber. A vacuum pump740, e.g., a one or two stage mechanical dry pump and/or turbomolecularpump, may be used to draw process gases out of the process chamber 724and to maintain a pressure within the process chamber 724. For example,the vacuum pump 740 may be used to evacuate the lower sub-chamber 703during a purge operation of ALE. A valve-controlled conduit may be usedto fluidically connect the vacuum pump to the process chamber 724 so asto selectively control application of the vacuum environment provided bythe vacuum pump. This may be done employing a closed-loop-controlledflow restriction device, such as a throttle valve (not shown) or apendulum valve (not shown), during operational plasma processing.Likewise, a vacuum pump and valve controlled fluidic connection to thecapacitively coupled plasma processing chamber may also be employed.

During operation of the apparatus 700, one or more process gases may besupplied through the gas flow inlets 760 and/or 770. In certainembodiments, process gas may be supplied only through the main gas flowinlet 760, or only through the side gas flow inlet 770. In some cases,the gas flow inlets shown in the figure may be replaced by more complexgas flow inlets, one or more showerheads, for example. The Faradayshield 749 and/or optional grid 750 may include internal channels andholes that allow delivery of process gases to the process chamber 724.Either or both of Faraday shield 749 and optional grid 750 may serve asa showerhead for delivery of process gases. In some embodiments, aliquid vaporization and delivery system may be situated upstream of theprocess chamber 724, such that once a liquid reactant or precursor isvaporized, the vaporized reactant or precursor is introduced into theprocess chamber 724 via a gas flow inlet 760 and/or 770.

Radio frequency power is supplied from the RF power supply 741 to thecoil 733 to cause an RF current to flow through the coil 733. The RFcurrent flowing through the coil 733 generates an electromagnetic fieldabout the coil 733. The electromagnetic field generates an inductivecurrent within the upper sub-chamber 702. The physical and chemicalinteractions of various generated ions and radicals with the wafer 719etch features of and deposit layers on the wafer 719.

Volatile etching and/or deposition byproducts may be removed from thelower sub-chamber 703 through port 722. The chuck 717 disclosed hereinmay operate at elevated temperatures ranging between about 10° C. andabout 250° C. The temperature will depend on the process operation andspecific recipe.

Apparatus 700 may be coupled to facilities (not shown) when installed ina clean room or a fabrication facility. Facilities include plumbing thatprovide processing gases, vacuum, temperature control, and environmentalparticle control. These facilities are coupled to apparatus 700, wheninstalled in the target fabrication facility. Additionally, apparatus700 may be coupled to a transfer chamber that allows robotics totransfer semiconductor wafers into and out of apparatus 700 usingtypical automation.

In some embodiments, a system controller 730 (which may include one ormore physical or logical controllers) controls some or all of theoperations of a process chamber 724. The system controller 730 mayinclude one or more memory devices and one or more processors. Forexample, the memory may include instructions to alternate between flowsof modification chemistry such as a chlorine-containing modificationchemistry and a removal gas such as argon, or instructions to ignite aplasma or apply a bias. For example, the memory may include instructionsto set the bias at a power between about 0V and about 200V during someoperations. In some embodiments, the apparatus 700 includes a switchingsystem for controlling flow rates and durations when disclosedembodiments are performed. In some embodiments, the apparatus 700 mayhave a switching time of up to about 500 ms, or up to about 750 ms.Switching time may depend on the flow chemistry, recipe chosen, reactorarchitecture, and other factors.

In some embodiments, disclosed embodiments can be integrated on a MSSD(Multi-Station-Sequential-Deposition) chamber architecture in which oneof deposition stations can be replaced by an ALE station to allow anintegrated deposition/etch/deposition process using a similar chemistryfor better fill and faster throughput capability.

In some implementations, the system controller 730 is part of a system,which may be part of the above-described examples. Such systems caninclude semiconductor processing equipment, including a processing toolor tools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be integrated intothe system controller 730, which may control various components orsubparts of the system or systems. The system controller 730, dependingon the processing parameters and/or the type of system, may beprogrammed to control any of the processes disclosed herein, includingthe delivery of processing gases, temperature settings (e.g., heatingand/or cooling), pressure settings, vacuum settings, power settings,radio frequency (RF) generator settings, RF matching circuit settings,frequency settings, flow rate settings, fluid delivery settings,positional and operation settings, wafer transfers into and out of atool and other transfer tools and/or load locks connected to orinterfaced with a specific system.

Broadly speaking, the system controller 730 may be defined aselectronics having various integrated circuits, logic, memory, and/orsoftware that receive instructions, issue instructions, controloperation, enable cleaning operations, enable endpoint measurements, andthe like. The integrated circuits may include chips in the form offirmware that store program instructions, digital signal processors(DSPs), chips defined as application specific integrated circuits(ASICs), and/or one or more microprocessors, or microcontrollers thatexecute program instructions (e.g., software). Program instructions maybe instructions communicated to the controller in the form of variousindividual settings (or program files), defining operational parametersfor carrying out a particular process on or for a semiconductor wafer orto a system. The operational parameters may, in some embodiments, bepart of a recipe defined by process engineers to accomplish one or moreprocessing steps during the fabrication or removal of one or morelayers, materials, metals, oxides, silicon, silicon dioxide, surfaces,circuits, and/or dies of a wafer.

The system controller 730, in some implementations, may be a part of orcoupled to a computer that is integrated with, coupled to the system,otherwise networked to the system, or a combination thereof. Forexample, the controller may be in the “cloud” or all or a part of a fabhost computer system, which can allow for remote access of the waferprocessing. The computer may enable remote access to the system tomonitor current progress of fabrication operations, examine a history ofpast fabrication operations, examine trends or performance metrics froma plurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the system controller 730 receivesinstructions in the form of data, which specify parameters for each ofthe processing steps to be performed during one or more operations. Itshould be understood that the parameters may be specific to the type ofprocess to be performed and the type of tool that the controller isconfigured to interface with or control. Thus as described above, thesystem controller 730 may be distributed, such as by including one ormore discrete controllers that are networked together and workingtowards a common purpose, such as the processes and controls describedherein. An example of a distributed controller for such purposes wouldbe one or more integrated circuits on a chamber in communication withone or more integrated circuits located remotely (such as at theplatform level or as part of a remote computer) that combine to controla process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, an ALDchamber or module, an ALE chamber or module, an ion implantation chamberor module, a track chamber or module, and any other semiconductorprocessing systems that may be associated or used in the fabricationand/or manufacturing of semiconductor wafers.

CONCLUSION

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe appended claims. It should be noted that there are many alternativeways of implementing the processes, systems and apparatus of the presentembodiments. Accordingly, the present embodiments are to be consideredas illustrative and not restrictive, and the embodiments are not to belimited to the details given herein.

1. A method of etching a metal on a substrate, the metal being selectedfrom tungsten (W) and cobalt (Co), comprising: (a) exposing a surface ofthe metal to a halide chemistry to form a modified halide-containingsurface layer; and (b) applying a bias voltage to the substrate whileexposing the modified halide-containing surface layer to a plasma tothereby remove the modified halide-containing surface layer.
 2. Themethod of claim 1, wherein the plasma is an argon plasma and the biasvoltage in (b) is between about 50 Vb and 80 Vb.
 3. The method of claim1, wherein (a) comprises exposing the surface of the metal to a plasma.4. The method of claim 3, wherein a bias is applied to the substrateduring (a).
 5. The method of claim 3, wherein the bias voltage during(a) is equal to or less than 100 Vb.
 6. The method of claim 3, whereinthe bias voltage during (a) is equal to or less than 50 Vb.
 7. Themethod of claim 1, wherein the metal is tungsten (W).
 8. The method ofclaim 7, wherein (a) comprises exposing the surface of the metal to achlorine-containing plasma.
 9. The method of claim 8, wherein thesubstrate temperature during (a) is less than 150° C.
 10. The method ofclaim 8, wherein the chlorine-containing plasma is generated from aCl₂/BCl₃ mixture.
 11. The method of claim 10, wherein the Cl₂/BCl₃mixture is between 0.5% and 10% (volumetric) BCl₃.
 12. The method ofclaim 1, wherein the metal is cobalt (Co).
 13. The method of claim 1,wherein (a) is performed without etching the surface of the metal. 14.An apparatus for processing semiconductor substrates, the apparatuscomprising: a process chamber comprising a showerhead and a substratesupport, a plasma generator, and a controller having at least oneprocessor and a memory, wherein the at least one processor and thememory are communicatively connected with one another, the at least oneprocessor is at least operatively connected with flow-control hardware,and the memory stores machine-readable instructions for: (i) introducinga halide-containing gas to modify a tungsten surface; and (ii)introducing an activation gas and igniting a plasma to etch at leastpart of the modified surface of tungsten.
 15. The apparatus of claim 14,wherein the memory further stores machine-readable instructions forigniting a plasma during (i).
 16. The apparatus of claim 14, wherein thehalide-containing gas is a chlorine-containing gas and memory furtherstores machine-readable instructions for maintaining a temperature ofthe substrate support at less than 150° C. during (i).
 17. The apparatusof claim 14, further comprising a direct current source to bias thesubstrate support, and the memory further stores machine-readableinstructions for setting the bias voltage less than about 80 Vb during(ii).
 18. The apparatus of claim 14, wherein the memory further storesmachine-readable instructions for repeating (i) and (ii) in cycles.